The present invention relates to an intermediate medium with a rubber top layer which contains a conductive material for use as a temporary image support in an imaging device or system. The imaging device uses the intermediate medium of this kind as the temporary image support.
Imaging techniques in which an image is formed on a temporary image support with a rubber top layer, and said image is transferred under pressure, possibly combined with a supply of heat, to a final receiving material, are known in various forms. In one very well known embodiment, a toner powder image is formed on a re-usable imaging element, such as a photoconductive element, a magnetic imaging element or an electrostatic imaging element containing a dielectric image receiving layer, and said toner powder image is transferred under pressure to an intermediate medium as specified above. The toner powder image is heated on the intermediate medium to make the toner powder tacky, whereafter in a second pressure transfer zone the tacky image is transferred and at the same time fixed on a final receiving support. The latter is heated if necessary before being introduced into the pressure transfer zone. After the image transfer in the second pressure transfer zone, an additional fixing step can take place if necessary to provide optimal fixing of the image on the final image receiving support. Also, in addition to or instead of the additional fixing step, other finishing operations can take place, for example, a gloss treatment. After-treatments of this kind are carried out particularly in the case of (multi-)color images.
Other imaging processes in which intermediate media with a rubber top layer can be used, are processes in which liquid ink or melted ink (hot melt ink) directly form an image on the top layer by means of an ink jet print head and the image is then transferred to the final receiving material.
The rubber top layer of the intermediate medium must have good mechanical and chemical permanency and should particularly be insensitive to the (low-melting) substances (waxes, plasticizers, etc.) released from the receiving materials, particularly receiving papers. The rubber must also have a certain electric conductivity to obviate electrostatic charges. Conventional rubbers for forming such a top layer are silicone rubbers and perfluoropolyether rubbers (PFPE-rubbers).
NL-A 1 001 471 proposes an intermediate medium wherein the rubber is a perfluoropolyether (PFPE) rubber. The top layer containing the PFPE-rubber described therein gives high resistance to the transfer of low-melting impurities. A process for the preparation of a PFPE-rubber by curing a lengthened-chain bifunctional PFPE-oil is described. In one embodiment, furnace black is added as a filler and conductive material to the PFPE-oil, whereafter thermal curing is carried out. In addition, a process is described for the preparation of the lengthened-chain PFPE-oils used as starting material, in which process a PFPE-oil having a weight-averaged molecular weight (Mw) in the range from 1500 to 3000 g/mol is reacted with a lengthened-chain agent selected from the group of di-acid chlorides and di-isocyanates.
One disadvantage of the embodiment of NL-A 1 001 471, in which furnace black is contained in the PFPE-rubber-containing top layer, is that the conductivity of the PFPE-rubber cannot be adjusted within a required bandwidth and the PFPE-rubber is therefore not anti-static. Another disadvantage is that the conductivity with furnace black in the antistatic PFPE-rubber is not stable. Deformation of the PFPE-rubber in fact causes the conductive furnace black paths to be broken. Yet another disadvantage is the difficulty of curing with UV radiation a PFPE-oil with which furnace black has been mixed.
In addition, the prior art makes a number of proposals according to which, in addition to furnace black, other conductive materials such as intrinsically conductive polymers, can be included in the top layer.
For example, U.S. Pat. No. 5,629,094 relates to a transfer material support consisting of a substrate and a top layer. The substrate preferably consists of a resin such as a polyester, polycarbonate, polyvinylidene fluoride, Teflon, polyurethane or polyacetate. The top layer contains a polyester resin, a hardened resin and a silicone polymer. This top layer can also contain polycarbonate, polyamide, polyacrylate, polyoxymethylene, polyphenylene oxide, polyphenylene sulphide, polyethylene, polypropylene, polystyrene, a copolymer of ethylene and propylene, a copolymer of styrene and butadiene, and so on. In addition, the top layer or the substrate may contain conductive materials such as metal powder, metal oxides, gas black, graphite, carbon fibers, organic or inorganic electrolytes and intrinsically conductive polymers such as polypyrrole or polyaniline.
U.S. Pat. No. 5,534,581 describes a transfer material support consisting of a copolycarbonate resin and conductive particles. The conductive particles comprise furnace black, metal oxides or intrinsically conductive polymers, such as polyaniline, polythiophene and polyacetylene. The conductive particles are dispersible in high concentration in the copolycarbonate resin.
U.S. Pat. No. 5,430,073 relates to a process for the preparation of intrinsically conductive polymers comprising in situ activation of precursor monomers whereby activated monomers are obtained which polymerize in the presence of a catalyst. Polymerization without activation of the precursor monomers is prevented. The intrinsically conductive polymers can, for example, be formed after mixing the precursor monomers in a polymer matrix. The intrinsically conductive polymers which are prepared with this process comprise polypyrrole, polythiophene and polyfurane which may or may not be substituted and mixtures of two or more of these polymers.
The object of the present invention is to include an intrinsically conductive polymer as a conductive material in a PFPE or silicone rubber, instead of furnace black, to ensure that a rubber is formed which is antistatic. Intrinsically conductive polymers, however, are insoluble in the rubber oil (PFPE or silicone oil) used as starting material. The present invention thus provides an intrinsically conductive polymer which is so modified that it can be combined with the rubber oil.
Accordingly, the present invention relates to an intermediate medium for use as a temporary image support in an imaging device, as described in the preamble, wherein the conductive material is an intrinsically conductive polymer so modified that it can be combined with the rubber oil.
PFPE-rubber or silicone rubbers can be used as the rubber. The preferred PFPE-rubber is as described inter alia in NL-A 1 001 471.
Conventional polymers, inter alia, as described in U.S. Pat. Nos. 5,629,094; 5,534,581 and 5,430,073, can be used as intrinsically conductive polymer. Examples are polyaniline, polypyrrole, polythiophene. A very suitable polymer is a modified polyaniline. The conductive polymer can be modified in various ways.
For example, a conductive polymer can be used that is doped with a PFPE-carboxylic acid. The PFPE-carboxylic acid preferably has the formula:
F3C[(OCF2xe2x80x94)pxe2x80x94(OCF2CF2xe2x80x94)q]OCF2xe2x80x94COOH
where p and q are in the range of 5 to 9. An advantage of such a modified conductive polymer is that a high intrinsic conductivity and good miscibility in a PFPE-oil used as a starting material can be obtained.
Preferably, the polyaniline used is modified by substituting it on the aromatic ring with a PFPE-chain. Particularly preferred is the use of a modified polyaniline which is a copolymer formed by the polymerization of aniline and aniline substituted on the aromatic ring with a PFPE-chain. The PFPE-chain is preferably a linear [(OCF2)m(OCF2Cxe2x80x94F2)n] chain where m and n are in the range of 9 to 13. One advantage of such modified polyanilines is that very good miscibility in a PFPE-oil used as a starting material can be obtained.
The homopolymers or copolymers of aniline substituted with a PFPE-chain can be further modified by doping them with a PFPE-carboxylic acid as described hereinbefore. An advantage of such a modified polyaniline is that when it is mixed in a PFPE-oil used as starting material, high conductivity is transferred to the PFPE-rubber.
The PFPE-chains of the homopolymers or copolymers of aniline substituted with a PFPE-chain can be provided with an acrylate group. An advantage of such a modified polyaniline is that when it is combined in a PFPE-rubber via the acrylate group, an accurate, adjustable and stable conductivity of the PFPE-rubber is obtained together with a wide choice with respect to the curing methods.
The process for the preparation of the modified polyaniline according to the present invention comprises the following reaction steps.
First Reaction Step 
In this reaction step, a fluoridized oil of formula 1 is converted with 0.5 equivalent of a base MB into the salt thereof having the formula 2.
The fluoridized oil used is preferably a fluoridized oil in which in formula 1 PFPE denotes 
where OCF2 and OCF2CF2 groups are randomly distributed. The base used is preferably an alkali metal oxide, for example potassium tert.butoxide, which yields the alkali metal salt of formula 2. There is no need to use a solvent to perform the reaction, but if required it can be used to bring the viscosity of the reaction mixture to a preferred level. If a solvent is used, it is preferably a non-reactive fluoridized solvent.
The salt of formula 2 is then reacted with nitrobenzene which, on the ortho or meta position, is substituted with a halogen atom X, giving a compound of formula 3. The halogen atom X is preferably a fluorine atom.
The compound of formula 3 is then reduced to a compound of formula 4, with the use of a catalyst system. A preferred catalyst system consists of Fe(II-I)Cl3, carbon and hydrazine hydrate. The solvent used is preferably a non-reactive fluoridized solvent.
The synthesis of compounds of formula 4 is described in T. Hirashime, O. Manare, Chemistry Letters, 1975, pages 259-260.
Second Reaction Step
In this reaction step, the formula 4 compound is polymerized to a formula 5 homopolymer by the use of a catalyst system: 
where PFPE has the above-mentioned meaning.
The catalyst system used is preferably a system consisting of 30% hydrochloric acid and ammonium persulphate. The solvent used is preferably a non-reactive fluoridized solvent.
The value of the length of the formula 5 homopolymer shown by o depends greatly on the polymerization conditions used.
The copolymer of PFPE-modified aniline and non-modified aniline can be prepared by adding aniline to the formula 4 compound before polymerization. The resulting copolymer is a random block copolymer of blocks of polyaniline and PFPE-modified polyaniline.
Aniline is not soluble in the formula 4 compound or in a fluoridized solvent.
Consequently, the copolymerization of aniline and the formula 4 compound proceeds via a heterogeneous mechanism, i.e. copolymerization takes place at the interface of the separate phases. In addition, quantum mechanics calculations have shown that aniline is more reactive in the polymerization reaction than the formula 4 compound. Consequently, a polyaniline fraction, a fraction of the formula 5 homopolymer and a copolymer fraction can be formed during the copolymerization reaction.
The copolymerization process can be controlled by varying the concentration and rates of feed of the monomers. The interface between the fluoridized solvent phase and the aqueous phase can be enlarged by stirring. In addition, the length of the various blocks in the copolymer can be controlled by varying the rate of polymerization in the separate phases.
The PFPE-modified homopolymer or copolymer has a higher miscibility in an acrylate-PFPE-oil than a non-modified polyaniline.
Third Reaction Step
In this reaction step, the formula 5 homopolymer is doped with a dopant having the formula
R1COOH
where R1 denotes a fluoroalkyl group, resulting in a homopolymer of formula 6
where PFPE has the above-mentioned meaning. The dopant used is an agent which protonizes the basic nitrogen atom of the homopolymer, the anion of the dopant forming an ionogenic bond with the protonized nitrogen atom. The anion produces an electron deficiency in the polymer chain, which provides electron conductivity in the chain. The maximum and optimal percentage of protonized nitrogen atoms is 50 mol %.
The dopant used is preferably a fluoridized carboxylic acid. It is more preferable to use a fluoridized carboxylic acid in the formula of which R1 denotes 
Doping of the copolymer from the second reaction step can be carried out in the same way as for the homopolymer.
Doping is needed to obtain conductivity and an increased miscibility in a PFPE oil of the homopolymer or copolymer. It is assumed that a doped homopolymer or copolymer consists of blocks which conduct satisfactorily, i.e. those in which the nitrogen atoms are protonized, and blocks of less or no conductivity.
Fourth Reaction Step
In this possible reaction step the PFPE chain of the formula 6 homopolymer from the third reaction step is terminated with an acrylate group by means of an alkenoyl chloride with hydrochloric acid being split off, giving a homopolymer of formula 7
where R1 has the above-mentioned meaning and R2 denotes 
where PFPE has the above-mentioned meaning. Preferably, the alkenoyl halide used is propenoyl chloride.
Termination with an acrylate group of the copolymer from the third reaction step can be carried out in the same way as for the homopolymer.
By termination with an acrylate group the intrinsic conductivity of the homopolymer or copolymer is not changed. Termination with an acrylate group, however, is needed if it is desirable to combine the homopolymer or copolymer with the PFPE-rubber. By such a combination the homopolymer or copolymer becomes a fixed part of the rubber and an interpenetrating network is formed. This can be desirable, for example, if the R1 and R2 groups form a sol fraction which has adverse effects on the visco-elastic properties of the PFPE-rubber.
It is possible to carry out the termination with an acrylate group in an earlier stage, for example, directly after the polymerization in reaction step 2. It is also possible to perform the termination in a later stage, for example, after the mixing of the homopolymer or copolymer into an acrylate-PFPE oil.
The resulting homopolymer or copolymer is then mixed into a PFPE-oil terminated with acrylate groups (hereinafter referred to as xe2x80x9cacrylate-PFPE-oilxe2x80x9d) having the formula
CH2xe2x95x90CHxe2x80x94(CO)xe2x80x94Oxe2x80x94PFPExe2x80x94Oxe2x80x94(CO)xe2x80x94CHxe2x95x90CH2
where PFPE has the above-mentioned meaning. The fluoridized R1-groups and R2-groups of the polymer have a great interaction with the acrylate-PFPE-oil so that the miscibility therein is high.
The mixture of the homopolymer or copolymer and the acrylate-PFPE-oil is then cured. UV-radiation or thermal curing can be applied. Curing is performed in accordance with NL-A 1 001 471, the content of which is incorporated herein by reference. It will be clear that instead of acrylate group termination it is possible to introduce any other reactive group provided said group is sufficiently reactive, under the reaction conditions selected, with respect to reactive groups already present or incorporated in the rubber-oil. Examples of other reactive groups suitable for termination are triethoxy, epoxy, hydroxyl, cyanate and isocyanate groups.
In yet another embodiment of the present invention, the intrinsically conductive polymer of the top layer is a PFPE-carboxylic acid doped, non-modified polyaniline. A polyaniline of this kind is obtained in the manner described above for the third reaction step subject to the condition that polyaniline is used as a polymer.
The PFPE-carboxylic acid doped polyaniline can also be prepared in the following manner. Firstly, aniline is mixed in an acrylate-PFPE-oil and then this mixture is cured as described above, yielding a PFPE-rubber. The aniline present in the PFPE-rubber is then polymerized oxidatively to form polyaniline and doped by immersing the rubber in an acidic oxidator solution with PFPE-carboxylic acid.